Preparation of blast holes to receive an explosive charge



M r h W55 1.. P. BARLOW ETAL PREPARATION OF BLAST HOLES TO RECEIVE AN EXPLOSIVE CHARGE 2 shets-sheet 1 Filed Dec.

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h 22, 1955 P. BARLOW ET AL PREPARATION OF BLAST HOLES TO RECEIVE AN EXPLOSIVE CHARGE Filed Dec. 28, 1.953

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ATTORNEYS United States Patent C PREPARATION OF BLAST HOLES TO RECEIVE AN EXPLOSIV E CHARGE Lester P. Barlow, Stamford, Conn., and Gale H. Brainard, Huntington Woods, Mich.

Application December 28, 1953, Serial No. 400,649

11 Claims. (Cl. 10223) This invention relates to the preparation of blast holes to receive an explosive charge, more particularly, blast holes which are very irregular in contour, such as those in very hard rock resulting from a burned hole, as distinguished from a drilled hole.

Taconite iron rock is so hard that a technique has had to be developed for making blast holes whereby the rock is perforated with a burner rig. Oxygen gas and fuel oil are used in the burner to burn the hole, which together with a stream of water directed on the hot rock, chips the rock, and steam, generated as the result of the flame directed onto the rock, blows the rock chips out of the hole as the hole is burned. The blast hole produced by this technique presents a very rough contour and the diameter varies throughout the length. Such an irregular condition precludes the fitting of explosive cartridges into the hole so that some other explosive, particularly one that will flow into the hole, must be used. An explosive charge, such as a carbon crystalloid having a large coeflicient for the absorption of liquid oxygen, is very satisfactory for this purpose, but loading the blast hole such as described above presents many problems, particularly if water is present in the hole. It is usual that in a formation to be blasted, water presents a major problem. Water will flow into the holes from lateral cracks almost as fast as it can be pumped out. It is an object of this invention to prepare a rough hole formed by burning such that it will be of substantially constant diameter and smooth and continuous throughout its length. It is a further object of this invention to deal with the water problem and eliminate the water hazard, to facilitate the loading of the hole with a flowing charge such as described above.

Further and other objects will be apparent from a description of the accompanying drawings in which like numerals refer to like parts.

Fig. 1 is a sectional view of a typical hole burned through hard rock, showing the water level in the hole;

Fig. 2 shows a preliminary step of sealing off the lateral cracks in the side walls of the hole;

Fig. 3 shows the insertion of the freezing tube;

Fig. 4 shows the hole prepared for the reception of a flowing explosive charge;

Fig. 5 is an enlarged cross section of the freezing tube; and

Fig. 6 shows the way in which the freezing tube of the flexible type can be retracted on a reel from the hole.

Fig. l of the drawing shows a typical blast hole in a very hard rock formation which results from burning the hole as described above.

The rock formation 1 has lateral cracks or fissures 2 radiating from the hole and some, such as 2, are connected with subterranean water sources and cause flooding of the blast hole to a water level, as shown at 3. Because of the rough contour and varying diameter of the hole, it is desirable to effect a smooth-walled hole in a manner that will seal off. the lateral cracks and the flow of water into the hole. This is accomplished, as shown in Fig. 2, by first dropping the inflatable bladder 4 into the hole to the water level 3 and inflating it by means of air tube 5 to block off the hole at the water level. A mass of moist plastic clay 6 is then placed in the hole on top of the bladder. An auger 31 is then passed down through the clay to force the clay into the lateral cracks and crevices in the rock formation, to thus afford a smooth-walled hole down to the water level. The clay is sufliciently plastic to hold its shape until If e Patented Mar. 22, 1955 freezing tube 7 is inserted in the hole. Auger 31 will puncture bladder 4 to permit the passage of the freezing tube 7.

Freezing tube 7 will either be formed from concentric metal tubing for relatively shallow holes or from flexible tubing for deeper holes. Rigid metal tubing can be used to advantage because of the excellent heat trans fer as a freezing tube. Its use is limited only by the facility with which it can be handled. Depending upon equipment available, steel tubing can be handled for hole depths of about 40 feet. Over 40' it is advisable to use a flexible tube construction as the freezing tube. Such a freezing tube includes the metal cap 8 formed with concentric collars 9 and 10, to which are attached casings 11 and 12, respectively, which together form a downward central passage 17 and an annular return passage 18 for refrigerant. The top of cap 8 is formed with fittings 13 and 14 for the connection of inlet and outlet tubes to refrigerating equipment. Fitting 13 communicates with passage 16 and conducts refrigerant to passage 17 in casing 11, which is connected to collar 9. Fitting 14 receives refrigerant from annular passage 16 in cap 8, which communicates with return passage 18,

The casings 11 and 12 forming the freezing tube 7 are of laminated fabric construction. The casing 12 may be formed in any suitable manner to achieve a flexible tube with sutficient strength to prevent the pressure of the refrigerant within from distorting the tube. Casing 12 is shown as comprised of several laminated layers and may be of conventional hose construction in which inner and outer layers 19 have reinforcing fabric or cord layers 20 secured therebetween to make an integral walled structure. Casing 11 is shown comprising inner and outer layers 21 and 22 with a light reinforcing layer 23 therebetween. As the tube is formed, spacers 23 in the form of bosses are molded on the outer surface to in sure adequate spacing of tubes 11 and 12 to form return passage 18. The elastomeric material forming layers 19, 21 and 22 may be of any suitable material which will maintain its flexible physical characteristics at low temperatures.

When freezing tube 7 is formed by a pair of concentric metal casings, they may be secured to cap 8 in any suitable manner or the cap may be eliminated by having the inlet and outlet fittings welded to the metal casings in an integral structure. Spacers may be provided between the casings similar to spacers 24.

Freezing tube 7, of any construction in. accordance with this invention, is inserted in the hole and a refrigerant, such as brine, from a suitable refrigerating equipment (not shown) is pumped through the freezing tube until the water in the lower portion of the hole and moist clay in the upper portion are frozen solid to a point around the hole shown by lines 27 and 28 in Fig. 4. After the clay and water are solidified by freezing, any fluid, such as air, may be pumped in inlet 13 to force the remainder of the refrigerant through outlet 14. The temperature of the scavenging fluid will be above the freezing point of water and will warm the outer wall of tube 7 sufliciently to free it from the surrounding frozen moist clay and water. Tube 7 may then be withdrawn from the hole. This may be done in the case of the flexible tube construction by transferring cap 8 to a reel, such as 29, mounted on a shaft 30. The flexible tube 7 may be exhausted to a pressure less than atmospheric to collapse the tube to assist in withdrawing it from the hole when winding it on the reel.

By the method and apparatus described above, it will be possible to provide a smooth-walled hole in any blast hole, formed in any manner, regardless of the amount of water in the hole. The moist clay technique over the water level can of course be employed over any length of the hole and a controlled diameter hole provided which will permit uniform blast by a controlled amount of charge.

To charge a blast hole prepared as above described, it is preferred to pour into the hole a predetermined amount of liquid oxygen and then pour in carbon crystalloids in a powdered or granular form. As the carbon crystalloids hit the surface of the liquid oxygen, they will be chilled and sink in the hole, absorbing liquid oxygen as they settle. Thus, two individually harmless ingredients, namely, the carbon crystalloids and liquid oxygen, are combined in the blast hole and become an activated explosive charge.

The above described technique not only solves the problem of loading jagged holes and holes partly filled with water, but insures safety by first reducing the hole to a known diameter which will take a known quantity of charge and produce a known result, and secondly, by utilizing individually harmless ingredients which only become activated to produce an explosive charge when the carbon crystalloids absorb enough oxygen in the bottom of the blast hole. While other types of charge may be used to advantage in the smooth-walled hole prepared in accordance with the above described invention, such as cartridges or bagged carbon crystalloids, the preferred form of flowing in the powdered or granular form of carbon crystalloids permits a greater density of charge in the predetermined diameter of the hole. T

It is to be understood that certain changes, alterations, modifications and substitutions can be made without departing from the spirit and scope of the appended claims.

We claim:

1. The method of preparing an irregular bore hole for the reception of an explosive charge which comprises filling the bore hole with a moist plastic material, perforating said material throughout the depth thereof, inserting a tube into said perforation, and flowing a re frigerant through said tube to solidify said material-' around said tube, and subsequently removing said tube and loading said bore hole.

2. The method of preparing an irregular bore hole for the reception of an explosive charge which comprises filling the bore hole with a moist plastic material, per-" forating said material throughout the depth thereof, insetting a tube into said perforation, flowing a refrigerant within said tube to solidify said material around said tube, flowing a scavenging fluid through said tube at a temperature slightly higher than the freezing temperature of the moisture in said material, and removing said tube from 0 said hole.

3. The method of preparing an irregular bore hole for the reception of an explosive charge which comprises filling the bore hole with a moist plastic clay, perforating said clay throughout the depth thereof, inserting a tube into said perforation, flowing a refrigerant through said tube to solidify said clay around said tube, flowing a scavenging fluid through said tube at a temperature slightly higher than the freezing temperature of the moisture in said clay, and removing said tube from said hole.

4. The method of preparing an irregular bore hole partially filled with water for the reception of an explosive charge which comprises inserting a barrier at the water level in said hole, filling said bore hole above said barrier with a moist plastic material, perforating said ma- 35 terial throughout the depth thereof and said barrier, inserting a tube into said perforation and through the water to the bottom of the bore hole, flowing a refrigerant through said tube to solidify the water in the hole and said material around said tube, flowing a scavenging CO fluid through said tube at a temperature slightly higher than the freezing temperature of the water and the mois- Ellie in said material, and removing the tube from said 5. The method of preparing an irregular bore hole C5 partially filled with water for the reception of an explosive charge which comprises inserting an inflatable bladder at the water level in said hole, filling said bore hole above said bladder with a moist plastic clay, perforating said clay throughout the depth thereof and said bladder, inserting a tube into said perforation extending through the water to the bottom of the bore hole, flowing a refrigerant through said tube to solidify the water in the hole and the clay around said tube, flowing a scavenging fluid through said tube at a temperature slightly higher than the freezing temperature of the water and the mois- '4 ture in the clay, and removing the tube from said hole.

6. A freezing tube for'use in preparing a bore hole for the reception of an explosive charge comprising a cap having inner and outer concentric collars forming concentric chambers, an inlet fitting in communication with the chamber formed by the inner central collar and an outlet fitting in communication with the annular chamber formed between said collars, a flexible, smoothwalled casing of sufficient flexibility to permit said tube to be collapsed and withdrawn from the hole, said cas ing having one end closed and the other end secured to said outer collar, of a length substantially equal to the depth of the bore hole, and an inner flexible-walled casing secured to the inner collar extending within said outer casing to a point adjacent the closed end of said outer casing, whereby a centrally located inlet passage and an annular return passage surrounding said inlet passage are provided. 7

7. A freezing tube for use in preparing a bore hole for the reception of an explosive charge comprising a cap member, inlet and outlet fittings secured to said cap member, a flexible, smooth-walled casing of sufficient flexibility to permit said tube to be collapsed and withdrawn from the hole, said casing having one end closed and the other end secured to said cap member, of a length substantially equal to the depth of the bore hole, and

an inner flexible-walled casing secured to said cap member extending within said outer casing to a point adjacent the closed end of said outer casing, whereby a centrally located inlet passage and an annular return passage surrounding said inlet passage are provided.

8. The method of preparing a bore hole filled with fluid material for the reception of an explosive charge which comprises inserting a hollow tube into said bore hole through'said fluid material, flowing a refrigerant through said tube to solidify said material around said tube, flowing a fluid through said tube at a temperature slightly higher than the freezing temperature of the fluid material around the tube, and removing the tube from said hole.

9. The method of preparing a bore hole for the reception of an explosive charge which comprises filling the bore hole witha moist plastic material, perforating said material throughout the depth thereof, inserting a tube into said perforation, flowing-a refrigerant within said tube to solidify said material around said tube, flowing a scavenging fluid through said tube at a temperature slightly higher than the freezing temperature of the moisture in said material, and removing said tube from said hole.

10. The method of preparing a water-filled bore hole 'for the reception of an explosive charge, which comprises inserting an elongated member into said waterfilled bore hole, refrigerating said member in the hole to solidify the water around said member, increasing the temperature of said member to a temperature slightly higher than the freezing temperature of the water in the hole, and removing said member from the hole.

11. The method of casting an ice liner in an irregular water-filled bore hole for the reception of an explosive charge, which comprises inserting an elongated member into said water-filled bore hole, refrigerating said member in the hole to solidify the water around said member, increasing the temperature of said member to a temperature slightly higher than the freezing temperature of the Ivlvalter in the hole, and removing said member from the References Cited in the file of this patent UNITED STATES PATENTS 2,145,473 Billner Ian. 31, 1939 FOREIGN PATENTS 8,607 Great Britain June 8, 1916 of 1915 

